Recently, magnetic disk driving apparatuses are widely used as external memory apparatus of word processors, personal computers or other various information devices.
FIG. 22 is a cross-sectional view of a known magnetic head assembly used in a magnetic disk driving apparatus for a disk having two opposite recording surfaces.
In the same drawing, a magnetic head assembly totally designated by reference numeral 101 generally comprises a magnetic head carriage 102 and an arm 103, and is transported by a pulse motor (not shown) in the radial direction of a magnetic disk 105 along a guide shaft 104.
The magnetic head carriage 102 is molded from an insulative synthetic resin, and includes a magnetic head mounting portion 102a as a front extension thereof and a support portion 102 as a rear extension thereof. Reference numeral 107 denotes a lower magnetic head which is attached to the magnetic head mounting portion 102a via a mold case 108. Reference numeral 109 designates a lead wire extending from the lower magnetic head 107 and connected to an externally extending lead wire 111 via a relay terminal 110.
The arm 103 is molded from an insulative synthetic resin into the form of a plate shorter than the magnetic head carriage 102, and a leaf hinge spring 112 is partly embedded integrally in the rear portion of the arm 103. The arm 103 is swingingly mounted to the magnetic head carriage 102 by a screw engagement between the exposed end of the leaf hinge spring 112 and the support portion 102b. Reference numeral 113 refers to a screw which secures the leaf hinge spring 112, 114 to a fixture fitment which fixingly engages the screw 113, to a spacer 115, and to a mounting fitment 116. Reference numeral 117 denotes an upper magnetic head disposed at a position opposed to the lower magnetic head 107 on the magnetic head carriage 102 via a gimbal spring 118. Reference numeral 119 denotes a pivot which engages the back of the gimbal spring 118. Reference numeral 120 refers to a lead wire extending from the upper magnetic head 117 and connected to an externally extending lead wire 122 via a flexible printed board 121. 123 denotes a stress plate interposed between the mounting fitment 116 and the arm 103 to always resiliently bias the arm 103 toward the magnetic head carriage 102 so that the magnetic disk 105 is closely sandwiched between the lower magnetic head 107 and the upper magnetic head 117.
When the magnetic disk 105 is not inserted into the magnetic head assembly 101 having the above-described arrangement, the arm 103 is lifted up by a lift mechanism (not shown) and held at a position rotated in arrow F direction about the swinging center at the junction with the leaf hinge spring 112, so as to hold the upper magnetic head 117 apart from the lower magnetic head 107 by a predetermined distance. When the magnetic disk 105 is inserted and clamped, the lift mechanism (not shown) releases the arm 103 from the lifted position. Responsively, the arm 103 drops with the energy of the stress spring 123, and the magnetic disk 105 is held closely between the lower magnetic head 107 and the upper magnetic head 117 for subsequent information writing or reading.
In order to ensure a stable recording and reproducing characteristic, a stable load pressure is required in the magnetic heads 107 and 117 which closely hold the magnetic disk 105 therebetween.
However, since the arm 103 in the prior art magnetic head assembly 101 is supported by the leaf hinge spring 112 in a cantilever fashion, a moment about the leaf hinge spring 112 is applied to the arm 103 due to an inertia caused by vibration components in the up-and-down direction (in the Z--Z direction of FIG. 22) upon a vibration or impulse against the magnetic head assembly 101, and the load pressure of the magnetic head 107 and 117 against the magnetic disk 105 varies.
Therefore, when the inertia applied to the arm 103 exceeds the load pressure of the magnetic heads 107 and 117 sandwiching the magnetic disk 105, the magnetic heads 107 and 117 fail to maintain reliable contacts with the magnetic disk 105, which apparently prevents a reliable recording or reproduction. Additionally, also the heads 107 and 117 are in acceptable contacts with the magnetic disk 105, any possible change in the load pressure of the magnetic head 107 or 117 against the magnetic disk 105 therebetween causes a variation in the frictional force between the magnetic heads 107-117 and the magnetic disk 105. This invites a vibration of the arm 103 in the rotating direction of the magnetic disk 105 or an uneven rotation of the magnetic disk 105, and these phenomena degrade the recording and reproduction characteristic.
In this connection, the Assignee of the present application, desiring a magnetic head assembly ensuring reliable recording and reproduction regardless of a possible vibration or impulse, proposes in Japanese Pat. Application No. Sho. 62-62559, which is Laid-Open publication No. Sho 63-229661 published on Sept. 26, 1988, a magnetic head assembly which includes an arm carrying a desired functional structure thereon and swingingly supported on a magnetic head carriage, which arm has a support point at a central portion in the length direction thereof to bear the functional part at front end side of the support point and bear a balancer at the rear end side of the support point to balance with the weight at the functional part carrying side.
This proposed magnetic head assembly is shown by a side elevation in FIG. 20 and a fragmentary perspective view in FIG. 21.
In FIG. 20 and 21, the magnetic head assembly 201 generally consists of a carriage 202, a support member 231 fixed to a support portion 202b of the carriage 202 by a screw 230, and an arm 232 swingingly supported by a pivot shaft 243 inserted in insertion holes 234a and 234b formed in the support member 231.
The arm 232, as shown in FIG. 21, is made by bending or folding a rigid metal plate such as aluminum alloy, and includes support points 232a and 232b upstanding at central portions thereof, a mounting portion 232c provided at the front end side of the support points 232a and 232b to engage a magnetic head apparatus 236 and a weight 238 provided at the read end side of the support points 232a and 232b to balance with the weight at the side of the front end side where the magnetic head apparatus is mounted. The mounting portion 232c and the support points 232a and 232b in the formerly proposed embodiment are, as shown in FIG. 20, coplanar with respect to the upper surface of the carriage 202 during loading, and the rear end side beyond the support points 232a and 232b inclines.
Other parts or members in the prior proposal of the Assignee which may be regarded as identical to those in the magnetic head assembly 101 of FIG. 22 are shown by the same reference numerals, and their explanation is omitted here.
In the magnetic head assembly 201 according to the prior proposed embodiment of the Assignee, when the magnetic disk is inserted for loading, the arm 232 pivots in arrow D direction about the pivot axle 243, and the magnetic heads 107 and 117 are separated to permit insertion of the magnetic disk 105 through an opening therebetween. In this case, however, corners 232f defined at the proximal ends of the upstanding support points 232a and 232b advance toward the magnetic disk 105 along an orbit line E. Therefore, when the magnetic disk 105 is in the form of a cartridge in which a magnetic disk is held in a hard case made from a hard synthetic resin, etc., the arm 232 must entirely be located in an upper position so that the corners 232f do not hit the case. However, when the arm 232 is located in an upper position, the thickness of the disk driving apparatus increases and prevents an improvement from the viewpoint of thickness reduction.
Since the prior art proposal of the Assignee supports the arm pivotably and uses the balancer, adverse effects of vibrations or impulses are certainly diminished. However, on the other hand, the structure for supporting the arm is complicated and requires an increased number of parts or members. More specifically, in FIGS. 20 and 21, the swinging support structure of the arm 232 requires the support member 231, the pivot axle 243 and screws and/or washers for fixing them, and further requires the weight 238 and its fixing member.
Beside this, either of the aforegoing prior art assemblies uses other arrangements not shown such as an engaging projection which is attached to the carriage and accepted in a helical feeding groove formed along the outer circumference of a screw shaft, a screw spring attached to the carriage to prevent the engaging projection from dropping out of the feeding groove, and a screw shaft resiliently sandwiched by the engaging projection and the stress spring so as to convert the rotation of the screw shaft into a linear movement of the carriage. However, when the screw shaft stops upon finishing transportation of the carriage, an inertia is applied to the carriage. This inertia causes a resilient deformation at the junction between the engaging projection and the carriage, and the carriage cannot stop immediately when the screw shaft stops. This inevitably elongates the settling time.